docs: def forward(angles, lengths):
      """ Link object as defined by the standard DH representation.
  
      :param list angles: angles of each joint
  
      :param list lengths: length of each segment
  
      :returns: a tuple (x, y) of the end-effector position
  
      .. warning:: angles and lengths should be the same size.
      """
      x, y = joint_positions(angles, lengths)
      return x[-1], y[-1]